I’d get kindle unlimited since a large number of books covering topics like this are available. Not every single one obviously, I still buy a lot of books. It’s a valid approach however.
I recently read every book an author from the Celestine light order wrote. I disagreed with his religious views 100% and still find sound basis in the work he presented and added a portion of it to my own practice.
Shook my at him telling me it could only be used for light. Much like a surgeon, who needs to know how to not kill someone on the operating table, if you can comprehend why and how it works, you can invert it to kill someone instead of helping them. Imagine that’s true with most things. If you can get to the essence of how and why you can take it for your own purposes- even when they are opposite of intended.